In a semiconductor light emitting device such as a light emitting diode (LED), when a current is passed therein, light of various wavelengths can be generated by electron-hole recombination at the junction of p-type and n-type semiconductors. Semiconductor light emitting devices have longer lifetime, lower driving voltage, and lower power consumption than light emitting devices of the filament type. Furthermore, semiconductor light emitting devices have various advantages such as no lighting delay time, high vibration resistance, and high surge breakdown voltage. Thus, as an easy-to-use light source, the demand therefor keeps growing.
Recently, a light emitting device based on group III nitride semiconductor for emitting light in the blue, short wavelength region has been spotlighted as a light source for illumination. However, the light emitting device based on group III nitride semiconductor has not yet satisfied the cost performance required for light sources for general illumination, and is required to provide higher optical output.
The semiconductor light emitting device includes an n-type semiconductor layer, a p-type semiconductor layer, and a light emitting layer provided therebetween. The light emitting layer is based on a quantum well structure capable of achieving high light emission efficiency. The quantum well structure is composed of a quantum well and barrier layers. In the quantum well, electrons and holes are recombined to emit light. The barrier layers sandwich the quantum well to form a well-type potential. Furthermore, the light emission efficiency can be increased by using a multi-quantum well (MQW) structure in which a plurality of well layers and barrier layers are stacked.
In the case of a light emitting device made of a nitride semiconductor material, it is known that lattice strain due to difference in lattice constant occurs between the semiconductor layers constituting the MQW structure and generates a piezoelectric field. The problem is that this decreases the electron-hole recombination probability in the quantum well and decreases the light emission efficiency. Thus, there is demand for a semiconductor light emitting device capable of reducing the lattice strain of the quantum well and increasing the light emission efficiency.